1. Field of the Invention
The present invention relates to a display device, and more particularly to a technique which is effectively applicable to through holes formed in a display region of a liquid crystal display device.
2. Description of the Related Art
Convention ally, as a display device which displays a video or an image, there has been known a liquid crystal display device which uses a liquid crystal display panel sealing a liquid crystal material between a pair of substrates.
In the liquid crystal display panel, one substrate out of a pair of substrates is generally referred to as a TFT substrate, and on a surface of a transparent substrate, a plurality of scanning signal lines and a plurality of video signal lines which stereoscopically intersects the plurality of scanning signal lines by way of an insulation layer are formed. Then, a region which is surrounded by two neighboring scanning signal lines and two neighboring video signal lines corresponds to one pixel region, and a TFT element, a pixel electrode and the like are arranged on each pixel region. Further, another substrate which forms a pair with the TFT substrate is generally referred to as a counter substrate.
When the liquid crystal display panel is, for example, of a drive method which is referred to as a vertical-electric-field method such as a TN method or a VA method, a counter electrode (also referred to as a common electrode) which faces the pixel electrode of the TFT substrate is arranged on a counter substrate side. Further, in case of a drive method which is referred to as a lateral electric field method such as an IPS method, for example, the counter electrode is formed on the TFT substrate side.
Further, the pixel electrode of the TFT substrate is electrically connected with a source electrode of the TFT element. Here, a one-layered or two-layered insulation film is interposed between the source electrode and the pixel electrode, and the pixel electrode is connected with the source electrode at an opening portion referred to as a through hole or a contact hole formed in the insulation film (for example, see patent document 1 (JP-A-11-326949)).
The TFT substrate and the counter substrate form an orientation film for controlling the direction (orientation) of liquid crystal molecules in a state that no potential difference exists between the pixel electrode and the counter electrode and an arrangement and an inclination of the liquid crystal molecules when the potential difference is generated between the pixel electrode and the counter electrode. The orientation film is formed on an interface with a liquid crystal material (a liquid crystal layer) of each substrate and, for example, is formed by applying rubbing treatment to a surface of a resin film made of polyimide which is formed to cover the whole display region constituted of a mass of the pixel regions.
Here, the pixel electrodes of the TFT substrate are formed by forming a transparent conductive film made of ITO on a whole surface of an insulation layer in which through holes (opening portions) are formed and, thereafter, by etching the conductive film. Here, an etching resist used in etching the conductive film is formed by applying a resist material in a liquid form on the conductive film by printing or coating and, thereafter, by exposing and developing the resist material.
However, in the liquid crystal display device of recent years, for example, along with the fining of the pixel region and the increase of a numerical aperture of the pixel region, a hole diameter of a through hole (opening portion) is decreased. Accordingly, for example, when the resist material in a liquid form is applied by printing or coating, the resist material in a liquid form hardly enters a recessed portion formed in a through hole portion. Accordingly, a defect is formed in the through hole portion of the etching resist which is formed by exposure and development and hence, the conductive film (ITO film) of the through hole portion is removed by etching performed subsequently. As a result, for example, there arises a drawback that a conductive failure is generated between the source electrode and the pixel electrode of the TFT substrate.
Further, in case of the TFT substrate, in forming the orientation film, the resin material in a liquid form is applied to the pixel electrode by printing or coating and, thereafter, the resin material is hardened (cured) by baking. Also in this case, for example, when the hole diameter of the through hole (opening portion) for connecting the pixel electrode with the source electrode is small, the printed resin material in a liquid form hardly enters the recessed portion formed in the through hole portion. Accordingly, there have been drawbacks that fine recessed defects are generated in the orientation film on the TFT substrate side, the orientation irregularities occur in the through hole portion, and leaking of light occurs.